Electrodeposition of Dysprosium in pyrrolidinium triflate ionic liquid at ambient temperature: Unraveling system efficiency and impact of solvation interplays on the reduction process

Atifi, Abderrahman; Baek, Donna L.; Fox, Robert V.

doi:10.1016/j.electacta.2021.138140

Cited by 11 publications

(29 citation statements)

References 53 publications

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“…At very small water traces (35 ppm), the voltammetry shows two reduction waves at about −1.3 and −3.35 V, respectively. The first wave exhibits significant chemical reversibility during the backward scan, with a half-potential of about −1.3 V. The positive potential and chemical reversibility of this wave are consistent with 1e – reduction to form Dy(II) intermediate . The second more negative wave, shouldering the cathodic decomposition of the pyrrolidinium ionic liquid, had no corresponding oxidation peak during the backward scan (to about +1.5 V vs Fc + /Fc).…”

Section: Resultsmentioning

confidence: 61%

“…While the heterogeneous speciation in our system was previously supported, exact factors altering the coordination spheres of Dy complexes were still unclear . Residual water traces in the dried ionic liquid are quantified at about 30 ppm, excluding the effect of ionic liquid impurities as a promoter for the heterogeneous speciation.…”

Section: Resultsmentioning

confidence: 69%

“…Previously, we reported NIR characteristics of the heterogeneous speciation at 1930 and 1970 nm, which were assigned to different coordination spheres of Dy complexes . In that report, the absorbance of the weakly IL-coordinated complex was shown to increase with the metal loading.…”

Section: Resultsmentioning

confidence: 85%

“…Dy reduction in ionic liquids has been reported to follow both consecutive two-step (1 + 2e – ) and single-step (3e – ) pathways. ,,, In the previous study, the voltammetry of Dy(OTf) 3 reduction in BMPyOTf was shown to exhibit two reduction waves and one main oxidation peak at about −2.3, −2.8, and 0 V, respectively . The forward features were assigned to reduction processes, leading to deposition of Dy metal on the surface, while the sharp oxidation peak during the backward scan is due to oxidative stripping of the Dy metal from the surface.…”

Section: Resultsmentioning

confidence: 96%

“…In previous work, we undertook an investigation exploring the electroreduction of dysprosium triflate Dy(OTf) 3 complex in pyrrolidinium triflate (BMPyOTf) ionic liquid . The electrodeposition of Dy(OTf) 3 in BMPyOTf was shown to exhibit two reduction waves.…”

Section: Introductionmentioning

confidence: 99%

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Water Interplays during Dysprosium Electrodeposition in Pyrrolidinium Ionic Liquid: Deconvoluting the Pros and Cons for Rare Earth Metallization

Orme

Baek

Fox

et al. 2021

ACS Sustainable Chem. Eng.

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The electrochemical production of rare earth metals (REMs) in ionic liquids (ILs) has received much attention as a promising, sustainable replacement to molten salt electrolysis. Water additives have been suggested as a promoting strategy for the ionic liquid process; however, the fundamental understanding of the interfacial processes required to assess the overall viability for REM production is lacking. In this regard, a full investigation of the impact of water on dysprosium (Dy) electrodeposition in pyrrolidinium triflate (BMPyOTf) ionic liquid was carried out. Water introduction was revealed to involve an interplay of implications on the electrodeposition process, including coordination, speciation, reduction pathways, interfacial dynamics, nucleation, and metal stability and purity. Under highly dry conditions, the reduction occurs at a very negative potential (−3.3 V) in a consecutive pathway, resulting in negligible metal electrodeposition (low rate and efficiency) at the electrode surface. Small water concentrations (<500 ppm) lead to partitioning of the Dy complex between water and IL-coordinated speciation, giving rise to an additional wave at a more positive potential (−2.4 V). Probing the heterogeneous Dy speciation by spectroscopic analyses enabled uncovering of the reduction mechanism and evaluation of the mass transport properties. In addition to lowering the reduction thermodynamics, water introduction also improved the nucleation, deposition rate, and faradic efficiency. Despite these benefits, stripping voltammetric analysis predicts substantial chemical reactivity of the deposited Dy metal with water additives and/or electrolyte components, under long timescales. Surface characterization of the obtained product confirmed the instability of Dy metal as an oxidized/fluorinated material and its limited purity (∼60%). Moreover, high water introduction triggered a fast hydrogen evolution reaction (HER), downgrading the robustness of system efficiency. The overall impact of water additives seems to engender both promoting and mitigating effects on electrochemical REM production in IL, requiring a specific technoeconomic assessment and/or more innovative strategies to be sought.

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Section: Resultsmentioning

confidence: 61%

Section: Resultsmentioning

confidence: 69%

Section: Resultsmentioning

confidence: 85%